Various melt-blowing processes have been described heretofore including those of Van A. Wente (Industrial and Engineering Chemistry, Volume 48, No. 8 (1956), Buntin et al. (U.S. Pat. No. 3,849,241), Hartmann (U.S. Pat. No. 3,379,811), and Wagner (U.S. Pat. No. 3,634,573) and others, many of which are referred to in the Buntin et al. patent.
Some of such processes, e.g. Hartmann, operate at high melt viscosities, and achieve fiber velocities of less than 100 m/second. Others, particularly Buntin et al. operate at lower melt viscosities (50 to 300 poise) and require severe polymer degradations to achieve optimum spinning conditions. It has been described that the production of high quality melt blown webs requires prior degradation of the fiber forming polymer (U.S. Pat. No. 3,849,241). At an air consumption of more than 20 lb. of air/lb. web substantially less than sonic fiber velocity is reached. It is known, however, that degraded polymer leads to poor web and fiber tensile strength, and is hence undesirable for many applications.
In co-pending application Ser. No. 138,860, filed Apr. 8, 1980 now U.S. Pat. No. 4,380,570, there is disclosed a process and apparatus for extruding through nozzles at high temperatures a molten polymer at low melt viscosity wherein the molten fibers are accelerated to near sonic velocity by gas being blown in parallel flow through small orifices surrounding each nozzle. The products produced thereby as well as in accordance with U.S. Pat. No. 3,849,241 are mostly polyolefins with only nominal molecular orientation. Fibers produced by the prior art melt-blowing processes are weak with unoriented molecular chain structure exhibiting no heat shrinkage characteristics and low values of birefringence.